This invention relates to a seal assembly for a roller cutter drill bit and more particularly to such a seal assembly positioned between sealing surfaces on a journal of the bit body and a roller cutter mounted on the journal for rotation.
A roller cutter drill bit includes the roller cutter mounted for rotation on a bearing journal of a drill body, and bearing means mounting the roller cutter on the bearing journal. A lubrication system is provided to supply lubricant to the bearing means, and sealing means are normally mounted between the roller cutter and the bearing journal on opposed bearing surfaces thereof to block the flow of lubricant outwardly past the bearing means and to block the passage of foreign matter such as drilling mud with entrained cuttings inwardly to the bearing means.
The sealing means generally employed heretofore has been elastomeric packing ring type seals such as "O" rings for example as shown in U.S. Pat. No. 3,397,927 or radially extended elastomeric rings such as shown in U.S. Pat. No. 3,765,495. These seals have required a large amount of deformation or squeeze when placed between the bearing surfaces of the roller cutter and journal to seal the relatively large clearances, to retain the lubricant within the bearing means, and to prevent the entry of foreign matter past the seal means. When such seals are provided with such a large amount of deformation or squeeze a substantial sliding friction is provided between the elastomeric sealing surface against the relatively rotating surface of the roller cutter or bearing journal. When relatively high rotational speeds are involved, a substantial amount of heat is generated thereby causing wear and decreasing the life of the seal and consequently the bearings.
In an attempt to increase the life of the seals in roller cutter drill bits, metal face seals have been utilized particularly under severe conditions of relatively high rotational speeds, high operating temperatures, or harsh downhole environment such as gasses detrimental to elastomers. One example of metal face seals for roller cutter bits is shown in U.S. Pat. No. 4,671,368 in which seal assemblies are positioned between sealing surfaces on the journal and the roller cutter to seal between relatively large clearances between the roller cutter and the bearing journal. Such a seal assembly has included a pair of rigid annular seals in an annular space between the journal and roller cutter with associated elastomeric seals between the annular rigid seals and adjacent sealing surfaces on the journal and roller cutter. The rigid annular seals are mounted for relative rotation in face to face sealing contact with each other and this sealing relation is maintained by a sealing force resulting from elastomeric seals urging the rigid seals toward each other. Thus, the elastomeric energizer seals provide a continuous sealing force for maintaining the rigid seals in face to face sealing relation with each other. In the event, however, of a permanent or compression set in the elastomeric seals which might occur at relatively high temperatures often prolonged periods of use, the sealing force exerted by the elastomeric seals against the sealing faces of the rigid seals may be reduced thereby providing a less effective seal between the sealing faces of the rigid annular seals.